Polycarbonates are useful, for example, for packaging materials and coatings and are of special interest because they are biodegradable.
Consideration has been given to a phosgene-free synthesis of polycarbonates using epoxides and carbon dioxide monomers and various catalysts, in most instances zinc-containing catalysts.
lnoue, S., et al., J. Poly. Sci. Lett. B7, 287-292 (1969) discloses use of a poorly defined heterogenous catalyst made by partially hydrolyzing diethyl zinc. The catalyst has a very low activity requiring days for polycarbonate production.
Aida, T., et al., J. Am. Chem. Soc. 105, 1304-1309 (1983) teaches an aluminum porphyrin catalyst which has very low activity (&lt;0.3 turnovers/hr).
Darenbourg, D. J., et al., Macromolecules, 28, 7577-7579 (1995) teaches a catalyst having the structure ##STR2## This catalyst provides higher activity (2.4 turnovers per hour) than previously described but said activity is still too low for a commercially competitive product. In the case of this catalyst, the ligands become part of the polymer chain end.
Super, M., et al., Macromolecules, 30, 368-372 (1997) discloses an ill defined catalyst made by reacting zinc oxide and ##STR3## This catalyst provided an activity of 8.4 turnovers per hour, which is higher than achieved before but which still is quite low. Moreover, it requires running the polymerization in supercritical CO.sub.2. In the case of this catalyst, the ligands become part of the chain end.
Moreover, conventional zinc (II) dicarboxylates and dialkoxides exhibit low activities and presumably lose their initial ligands during the polymerization reaction.
The catalysts heretofore exhibit polymerization rates that are far too low for an efficient industrial process. The polycarbonates made from epoxide and carbon dioxide up to now have not made much commercial impact because they are expensive due to time-consuming preparation because of the low activity of known catalysts.
Due to the inexpensive and accessible monomers used in the process (epoxides from olefins and O.sub.2, CO.sub.2) and the attractive properties and potential of polycarbonates, the development of a new, category of catalysts for this polymerization process is a significant scientific goal.